The present invention relates to liquid crystal display devices or transflective liquid crystal display devices having both reflective and transmissive mode, used for office automation (OA) equipment such as word processors and personal computers, mobile information terminals such as personal digital assistants and mobile telephones, or camcorders equipped with a liquid crystal monitor.
Liquid crystal display devices are classified broadly into those capable of displaying images in a reflective mode, those capable of displaying images in transmissive mode, and those of capable of displaying images in both reflective and transmissive modes and have been used widely as display devices for lap top computers or televisions because of their low-profile and light weight characteristics. In particular, the transflective liquid crystal display devices use a display mode capable of displaying images both in reflective and transmissive modes and thus can display images in a well-lighted area or a dark area and reduce the electric power consumption by switching to either one of the reflective and transmissive modes, depending on the brightness in the environment. Therefore, the transflective liquid crystal display devices have been used for various mobile information terminals.
The transmissive, reflective and transflective liquid crystal display devices in particular in the transmissive mode can not avoid problems concerning viewing angle such as reduced display contrast, changes in display color and reversed gradation occurring when viewed obliquely because of the refractive index anisotropy of the liquid crystal molecules and thus has been demanded to be improved in these regards.
For a transmissive liquid crystal display device using a TN mode (twisted angle of liquid crystal is 90 degrees), a method for solving these problems has been proposed and practically used wherein optical compensation films are disposed between the liquid crystal cell and each of the upper and lower polarizers.
For example, there are known some structures wherein an optical compensation film composed of a hybrid-aligned discotic liquid crystal or a nematic hybrid-aligned liquid crystalline polymer compound is disposed between the liquid crystal cell and each of the upper and lower polarizers (Patent Document Nos. 1 to 3 below).
For a transflective liquid crystal display device, it is necessary to dispose a circular polarizer comprising one or a plurality of uniaxially retardation film in displaying principle and a polarizer above or below the liquid crystal cell for the transmissive mode.
In order to enlarge the viewing angle of the transflective liquid crystal device in the transmissive mode, a method has been proposed and practically used wherein an optical compensation film aligned in a nematic hybrid orientation is used as a circular polarizer to be disposed between the liquid crystal cell and the backlight (see Patent Document Nos. 4 and 5).
(1) Patent Document No. 1: Japanese Patent Publication No. 2640083
(2) Patent Document No. 2: Japanese Laid-Open Publication No. 11-194325
(3) Patent Document No. 3: Japanese Laid-Open Publication No. 11-194371
(4) Patent Document No. 4: Japanese Laid-Open Publication No. 2002-31717
(5) Patent Document No. 5: Japanese Laid-Open Publication No. 2004-157454